რეზიუმე

The testing and development project "Amphibian habitats in an agricultural landscape" focusedon the testing of measures for conservation and development of typical amphibian populations inthe Central European cultural landscape. The project performed by the Zoologisches For-schungsmuseum A. Koenig (ZFMK) from may 2000 until October 2003, continued the survey of seven amphibian species in the “Drachenfelser Ländchen” near Bonn, which was accomplishedfrom 1988 to 1992 as well as from 1993 to 1995 in a former E+E-project “Cross-linking of am- phibian habitats”. It was based on the establishment of three artificial foil ponds in the year 1988as an addition to existing waters and the introduction of the great crested newt to two waters afew years later. During the following monitoring the practical measures were evaluated and theresults were used as a basis for recommendations for amphibian conservation. Due to its runningtime of 15 years with eleven years of amphibian survey the project belongs to the world-widerare long-term studies on amphibians. It was one of the few studies, in which more than one sin-gle waterbody and the demographic interactions of the inhabiting populations were examined.The aim of the project was to increase the understanding of amphibian population dynamics inagricultural ecosystems and to derive recommendations for the development and cross-linking of amphibian habitats. The population dynamics, population structure and dispersal of alpine newt(Triturus alpestris), smooth newt (T. vulgaris), great crested newt (T. cristatus), water frogs( Rana esculenta –complex), common frog (R. temporaria), agile frog (R. dalmatina) and com-mon toad (Bufo bufo) were recorded at five ponds from 1989 to 2003 and analysed with differentmethods and in respect of the following questions:
Long-term dynamics:
What do the population dynamics of the amphibian species look like?Which factors affect these dynamics? Are the waters suitable for the development of sus-tainable amphibian populations? Are there quality differences between natural and artifi-cial waters as breeding sites? Can artificial waters support and/or replace natural waters?
Age structure and survival rates:
How important are survival and recruitment for populationsof different species? Do the populations show typical age structures?
Dispersal and gene flow:
Does dispersal between ponds take place, and if so, at which amountand frequency? Does dispersal contribute to gene flow between waters and which factorsaffect it? Do immigration and emigration have demographic effects on the amphibian populations?
Evaluation and improvement of herpetological field methods:
What is the relative impact of invasive marking methods on the survival rates of different species? Are drift fences andfunnel traps effective enough for census investigations and do they alter natural move-ment behaviour of amphibians near the pond? Do wooden sticks, used as ladders for small terrestrial mammals to reduce their mortality? Do they affect the effectiveness of pitfall traps for amphibians?
Kapitel XI: Summary367
The seven species of amphibians showed large variations of population sizes and even larger fluctuations in reproductive success. There were no hints of a general population decline, as ob-served in many amphibian species in other regions ("global amphibian decline"). An overallnegative trend was observed only in the common toad, which population declined from severalthousand adults and ten thousands metamorphs per year to only a few adults with nearly no re- productive success. In contrast, alpine and smooth newts settled in all five waters and were in theend the most frequent species in the study area, with population sizes of several thousand ani-mals. The introduction of great crested newts was successful. The population finally developedto 60–150 individuals in the last project phase. After a sluggish settlement phase the water frogsalso established sustainable populations with up to 600 animals in the area.
Rana lessonae
wasthe dominating phenotype (80 %,
R.
kl.
esculenta
with 11 % and
R. ridibunda
less than 3 %).Population sizes and reproductive success of common and agile frog varied strongly withoutrecognisable long-term trend. The populations contained at last 300 adults of the common frogrespectively 800 individuals of the agile frog. With the establishment of the artificial ponds,smooth and alpine newts as well as agile and water frogs were promoted. For common toad,common frog and great crested newt the measures were less effective. Observed fluctuations in population sizes are probably due to density effects especially in the larval phase which becomesapparent in a reduced size of metamorphs and a reduced number of juveniles per female. Further reasons for deme size fluctuations might be the occasional desiccation of breeding ponds and predation by fish or by invertebrates. In contrast, interspecific competition could not be detected.Compared to the partially extreme high mortality in the phase from egg to metamorphosis, mor-tality of the adults of the four studied anuran species was moderate and mostly independent fromsex. Survival rates per year varied between 12 % (
Bufo bufo
) and 51 % (
Rana dalmatina
). An-nual reproduction was common in all four species. At least a few specimen reached an old ageand took part in reproduction until an age of eleven (common frog) respectively ten years (greatcrested newt, common toad, agile and water frogs). The moderate survival rates of
Trituruscristatus
in connection with constant population sizes and partially high juvenile output do notindicate negative anthropogenic effects whereas the very low survival rates of
Bufo bufo
(com- pared to literature) are remarkable and could not be explained.The relationship of recruitment and adult survival was estimated for common and agile frogs.Dependent on year and pond, these varying factors influence the population sizes, by sometimesneutralising each other, sometimes adding up. Agile frogs showed a lower adult mortality, amore regular reproductive success and recruitment than common frogs and seemed to pursue aK-strategy. The age structures of the brown frogs as well as of alpine and smooth newts showedthe typical distributions and generation times of the species. No serious gaps in recruitment werefound.Allozyme data and capture-mark-recapture analysis – applied to smooth and alpine newts – indi-cate a substantial and more or less continuous gene flow between breeding sites. F
ST
-values cal-culated from the allozyme data were very low (usually F
ST
<< 0,1) and suggest low differentia-
Kapitel XI: Summary368tion of demes, which were situated maximally 1.800 m of each other. Potential barriers, e. g.roads, showed a significantly reduced gene flow. The overall genetic variability of the two newtspecies does not seem to be reduced, and it is not likely that genetic load affect the fitness of theindividuals. However data for the smooth indicates a past time genetic bottleneck. Dispersal es-timates from capture-mark-recapture-analysis mainly support the results of the genetic methods.They show a substantial dispersal of experienced breeders between demes. The dispersal rates of adults within three years ranged between 4,5 % (alpine newt) and approx. 15 % (water frogs).This dispersion seems to be high enough to overcome local extinction and avoid negative influ-ence of isolation on individual fitness. A simulation of the dispersal probabilities of alpine andsmooth newts as a function of distance and population size reveals an estimate of minimum dis-tances for the supply of new ponds, which will be colonised with a given probability.The comparison of two marking methods (toe clipping and implantation of passive integratedtransponders) in anurans did not show differences in survival. Until further notice the applicationof both methods can therefore be recommended. Due to the higher error rate in toe clippingcaused by marking errors and problems in recognising the code the transponder implantation isto be preferred despite higher material costs.Because of the limited effectiveness of drift fences in most cases it is not possible to register allor nearly all individuals. The investigations show that the portion of captured individuals de- pends on the amphibian species, the characteristics of the ponds and the duration of the study.While the effectiveness of the drift fences for the newts ranged only between 50 and 80 %, it wassomewhat higher in the case of the anurans, with average values from 70 to 95 %. The use of durable drift fences clearly affects the amphibian movement and leads over several years to anaccumulation of animals within the fence. The necessity for durable drift fences should therefore be weighed out exactly; if necessary, other methods (e.g. aquatic funnel traps or temporary driftfences), which have no accumulating effect can offer similar capture efficiencies. The effective-ness of pitfall traps at drift fences is substantially reduced by wooden sticks, which are used toreduce small mammal mortality. This effect is higher in newts than in anurans. On the other hand, sticks can effectively reduce the mortality of small mammals and therefore should be usedwhenever possible.The long term data illustrate that large amphibian populations could sustain in intensively usedagrarian landscapes. Substantial fluctuations in population sizes and reproductive success aremainly consequences of the life history traits of amphibians and do not always express negativeman-made influences on populations. As long as suitable land habitats are present and source populations with many individuals exist in a distance of up to 2.000 m, even those amphibianspecies, which are believed to have small dispersal ranges such as the alpine and the smoothnewt, are able to colonise new ponds or prevent existing populations from extinction. In this casenew established ponds contribute effectively to the persistence of amphibian populations in alarger landscape area.